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Re: size variation of -0.04mm in X axis of every machined part

First, you would need to perform a mechanical-play test on that axis, if the resulting readings actually show that a little amount of play exists, you can try to help the machine using the related parameter(s), that process is called backlash compensation.

But depending on the machine's age/use/abuse, you could find a lot of play, in that case, further mechanical checks would be necessary, ballscrew wear, bearings, couplings, etc.

Re: size variation of -0.04mm in X axis of every machined part

Hi,
to me it looks like a programming type problem.
Using incremental commands in a sub program?
Looping?
To consistently change size the same amount in the same direction doesn't sound like a backlash problem.

Re: size variation of -0.04mm in X axis of every machined part

With a total variance of .0063" (.16mm) I'd be curious on what tolerance you're trying to hold?
Are you uni-directionally cutting this diameter? Have you verified your roughing routine and it's insert/cutter?
What about material? Are you holding better repeatability on other similar machines? Same process? Is your operator changing offsets based off of one sample? Are your operators re-cutting the part?

... I think backlash is a bit of a stretch to isolate and troubleshoot the machine as the problem.
Are you capable of holding tighter tolerances on other features?

Re: size variation of -0.04mm in X axis of every machined part

The fact that each subsequent run of the program varies
by exactly .04 is just too coincidental , and
points me to a programming/work offset issue.

Not knowing more about the machine (is this new or old, did
the problem just appear recently), I would also
look to see if there are macros being executed for tool
changes and or sub program calls. If so I'd troubleshoot
those as well.

Re: size variation of -0.04mm in X axis of every machined part

Originally Posted by camsys

The fact that each subsequent run of the program varies
by exactly .04 is just too coincidental , and
points me to a programming/work offset issue.

Not knowing more about the machine (is this new or old, did
the problem just appear recently), I would also
look to see if there are macros being executed for tool
changes and or sub program calls. If so I'd troubleshoot
those as well.

LOL - good catch cam - I totally missed that.
Yea, that's a smoking gun to the program or a programmed routine. Maybe a variable is being used and not reset?
It's NOT with your backlash comps if this pattern is that repeatable.

Re: size variation of -0.04mm in X axis of every machined part

This is o ften seen when using TNRC (G41\G42) and then having two lines of information in a row without axis motion - this cause unexplained axis accumulation errors. Try checking to see if you are using G42/G42 and if so make sure there are not two line in a row without axis motion prior to a G40
IE:
G42X___Z____
G50S5000
G96S300

Re: size variation of -0.04mm in X axis of every machined part

This is often seen when using TNRC (G41\G42) and then having two lines of information in a row without axis motion - this cause unexplained axis accumulation errors. Try checking to see if you are using G42/G42 and if so make sure there are not two line in a row without axis motion prior to a G40
IE:
G42X___Z____
G50S5000
G96S300

Re: size variation of -0.04mm in X axis of every machined part

Originally Posted by Tom69

This is often seen when using TNRC (G41\G42) and then having two lines of information in a row without axis motion - this cause unexplained axis accumulation errors. Try checking to see if you are using G42/G42 and if so make sure there are not two line in a row without axis motion prior to a G40
IE:
G42X___Z____
G50S5000
G96S300

Tom

Hi Tom,
I've never know that to be the case, and particularly there is no accumulation of error as stated by the OP when two or more consecutive non motion blocks are programmed in TNR compensation mode. If two or more non motion blocks are specified consecutively, the tool nose center comes to a position vertical to the programmed path of the preceding block at the end of the preceding block, but there is no accumulation of any error.

I agree with Doug and camsys that its likely to be some programming or Offset issue, but not TNR offset initiated, and Backlash does not present in the way described by the OP. If the OP uses G50 to set the coordinate system, then not cancelling the Tool Offset when the slides are sent back to the tool change position will definitely give the results indicated. In this case there is a continual and consistent drift of the tool change position by the amount of the tool wear offset.

Unfortunately, the OP is missing in action, so its hard to determine what the issue is without further information. One can only speculate.

Which size is it suppose to be? Tool T0303 @ 13.6? Or 13.55?
There are quite a few irrelevant moves and some basic bad code but, nothing that would suggest an accumulative error.

Try this;
Make a TEST program.
Put an indicator on the top of your spindle (or some other rigid location).
Using a tool - doesn't matter what kind, move the tool to the indicator and Zero the indicator and write down your ABSOLUTE position. (we'll call this your work offset)
G28U0
G00X25.Z25. (from your indicator Zero)
G98G01U-23.W-23.F200.
G01U-2.W-2.F20.
G04U2.0
G01U10.
G28U0
G28Z0
M99
%
Run this program a few times to see if it repeats.
If it does, add a tool change at the beginning and end and repeat the test.
Try to isolate where the error is originating.